Efficacy and Safety of Elexacaftor-Tezacaftor-Ivacaftor in the Treatment of Cystic Fibrosis: A Systematic Review

Elexacaftor/Tezacaftor/Ivacaftor (ELX/TEZ/IVA) is a new CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) modulator treatment, used over the last few years, which has shown an improvement in different clinical outcomes in patients with cystic fibrosis (CF). The objective of this study was a systematic research of the literature on the efficacy and safety of this CFTR modulator on patients with CF. A search of Pubmed was conducted for randomized clinical trials and observational studies published from 2012 to September 2022. The included full manuscripts comprised nine clinical trials and 16 observational studies, whose participants were aged ≥12 years or were children 6–11 years old with at least one Phe508del mutation and/or advanced lung disease (ALD). These studies reported that ELX/TEZ/IVA has a significant positive effect on the lung function of patients with CF, by ameliorating parameters such as FEV1, LCI, pulmonary exacerbations or sweat chloride concentration, increasing BMI and improving quality of their life. Its role in cystic fibrosis-related diabetes (CFRD) is not yet clear. It was found that this new CFTR modulator has an overall favorable safety profile, with mild to moderate adverse events. Further studies are needed for a deeper understanding of the impact of CFTR modulators on other CF manifestations, or the possibility of treating with ELX/TEZ/IVA CF patients with rare CFTR mutations.


Introduction
Cystic fibrosis (CF) is an autosomal recessive genetic disease, which affects approximately 70,000 people worldwide [1]. It is caused by mutations of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, which encodes for the CFTR protein, located on the apical surface of epithelial cells of multiple tissues (respiratory system, gastrointestinal tract, male reproductive organs, pancreas, sweat glands, etc.) and is responsible for chloride and bicarbonate transport across the epithelial surfaces. Defective CFTR protein leads to a decrease in chloride secretion and an increase in sodium absorption, followed by an osmotic uptake of water, provoking thick fluid secretions. In addition, diminished bicarbonate secretion is responsible for inadequate alkalization of pH and, though impairment of antimicrobial factors, of the surface liquid. As a result, chronic pulmonary inflammation and infection develop and bronchiectasis and progressive lung function decline, in association with impaired gastrointestinal function (bowel obstruction, hepatobiliary disease and pancreatic insufficiency), malnutrition and infertility [2][3][4].
There are more than 2000 CFTR sequence variants and approximately 350 of them are known to cause CF. Phe508del mutation is the most common mutation and 88% of patients have at least one copy [2,3]. CFTR mutations are classified into six categories according to the molecular mechanism of decreased functional expression: in class I mutations, the the first second (ppFEV 1 ), sweat chloride concentration (SCC), CFQ-R respiratory domain score (CFQ-R RD), body mass index (BMI), exacerbation rates, healthcare visits, and type and frequency of adverse events due to the treatment.
As far as observational studies are concerned, they must have included CF patients with Phe508del/Phe508del or Phe508del/Minimal Function genotypes, treated with triple combination therapy (Elexacaftor/Tezacaftor/Ivacaftor), controlled for a specific period of time and reporting at least one outcome related to our study (pulmonary function, BMI, CFQR, sweat chloride concentration, exacerbation rates, healthcare visits, glycemic status, adverse events of treatment).

Study Selection
This systematic search initially yielded 223 papers, all of which were published in the last decade, indicative of the recent development of these drugs. The keywords used to conduct the search were elexacaftor, tezacaftor, ivacaftor. Data were extracted by two researchers, who reviewed the search results independently. Any disagreements were resolved by consensus and discussion. The review was based on titles and abstracts and when the abstract was not helpful the full manuscript was reviewed. 223 articles were screened, 66 of which were excluded by title, and 157 were screened for eligibility. Finally, 25 articles met the eligibility criteria for inclusion (nine clinical trials and 16 observational studies). Figure 1 depicts the various steps of the data collection and selection process.

Efficacy of Elexacaftor-Tezacaftor-Ivacaftor
Pulmonary Efficacy and effect on sweat chloride concentration The most commonly used indicators of lung function in CF patients are the ppFEV 1 and the occurrence of pulmonary exacerbations (PEx). Another important tool is the Cystic Fibrosis Questionnaire-Revised Respiratory Domain (CFQ-R RD), which is a measure of subjective amelioration of pulmonary symptoms and quality of life. An alternative research measure of lung health is the Lung Clearance Index (LCI), usually reported as LCI 2.5 , which is a measure of ventilation inhomogeneity [7].
Migliorisi et al., using a small sample of patients (n = 26) with at least one Phe508del copy (Phe508del/Phe508del or Phe508del/MF genotypes) found out that, in one year, the ppFEV 1 of patients treated with the triple combination was augmented by 10-15 points, the number of pulmonary exacerbation was statistically significantly reduced (p < 0.05), 77% of the cases reported a diminished SCC and 100% of the cases showed an increase in the CFQ-R RD score [13]. Studying a different group in a phase 3 trial, namely 258 patients aged ≥12 years, with Phe508del/Gating mutation or Phe508del/Residual mutation genotypes, after a 4-week run-in period where they received IVA or IVA/TEZ, respectively, Barry et al. observed an increase by 3.5% (95% CI 2.2-4.7, p < 0.001) in ppFEV 1 , an absolute change in SCC by 23.1 mmol/lt (95% CI −26.1 to −20.2, p < 0.001), and an amelioration of CFQ-R RD score by 8.7 points (95% CI 5.3-12.1) through to week 8 with ELX/TEZ/IVA treatment compared to active control. Studying the role of genotype, the researchers assessed that, for patients with Phe508del/Gating mutation genotype, through to week 8 the mean increase in ppFEV 1 was 5.8 points (95% CI 3.5-8.0), the SCC diminished by 20 mmol/lt (95% CI −25.4 to −14.6) and the CFQ-R RD score increased by 8.9 points (95% CI 3.8-14.0) relative to active control. For patients with Phe508del/Residual mutation genotype through to week 8, the mean change in ppFEV 1 was 2% (95% CI 0.5-3.4), the mean change in SCC was −24.8 mmol/lt (95% CI −28.4 to −21.2), and the CFQ-R RD score was ameliorated by 8.5 points (95% CI 4.0-13.0) compared to the active control group [14].
In a phase 3b trial, conducted by Mall et al. with 121 young patients aged 6-11 years with Phe508del/MF genotypes, for subjects treated with ELX/TEZ/IVA the mean baseline LCI 25 was 10.26 units and the mean ppFEV 1 was 91.4%. After 24 weeks of treatment, there was a significant decrease in LCI 2.5 of 2.26 units (95% CI −2.71 to −1.81, p < 0.0001) and an increase in ppFEV 1 of 11 percentage points (95% CI 6.9-15.1, p < 0.001) for ELX/TEZ/IVA group versus placebo. The SCC in ELX/TEZ/IVA group diminished by 52.1 mmol/lt (95% CI −55 to −49.2) compared with a change of −0.9 mmol/lt (95% CI −3.8 to 2.0) in placebo group through week 24 [15]. Finally, Mainz et al. in a prospective study with 107 patients with at least one Phe508del mutation, as secondary endpoints observed that ppFEV 1 in those treated with ELX/TEZ/IVA for 24 weeks increased by 13 percentage points compared to baseline (p < 0.0001) [16].
Growth and Nutrition CFTR modulators have been effective in weight gain and BMI increase. Change in BMI was one of the secondary endpoints of the study conducted by Middleton et al., which noticed that patients ≥12 years receiving ELX/TEZ/IVA for 4 weeks experienced a BMI increase, with a mean treatment difference of 1.04 relative to the placebo group (95% CI 0.85-1.23, p < 0.001) [10]. The phase 3 study by Heijerman et al. revealed that Phe508del homozygous patients ≥12 years treated with ELX/TEZ/IVA had an improvement of BMI at week 4 of 0.60 kg/m 2 (95% CI 0.41-0.79, p < 0.0001) and a mean body increase of 1.6 kg (95% CI 1-2.1, p < 0.0001) compared with TEZ/IVA group [11]. In addition, Migliorisi et al. found out that patients ≥ 12 years old, with at least one Phe508del mutation treated with ELX/TEZ/IVA for one year, significantly increased their BMI, compared to the control group [13]. Furthermore, Mainz et al., in a prospective study with 107 patients, noticed that for children treated with ELX/TEZ/IVA the means for BMI-for-age z-scores increased at week 22 from −0.71 ± 0.19 to −0.29 ± 0.24 (p = 0.002) and the mean weight from 47 ± 2.1 kg to 51.4 ± 2.3 kg (p < 0.0001). In adults the mean BMI and weight increased by 8% compared to baseline, from 22.2 ± 0.3 kg/m 2 to 24 ± 0.4 kg/m 2 (p < 0.0001) and from 63.1 ± 1.3 kg to 68.2 ± 1.4 kg (p < 0.0001), respectively [16].
Other clinical parameters CF patients cope with multiple infections of the respiratory tract, which require frequent antibiotic use or even hospital admission. Miller et al. performed a case-crossover analysis which included 389 CF patients who began treatment with ELX/TEZ/IVA for a 15-week period and compared them with patients without treatment for the same period. The triple combination therapy revealed a decrease in the number of healthcare visits, −2.5 (95% CI −3.31 to −1.7), a change in patients' admissions, −0.16 (95% CI −0.22 to −0.1), a diminished number of visits related with infections, −0.62 (95% CI −0.93 to −0.31) and a change in distinct antibiotics prescribed, −0.78 (95% CI −1.03 to 0.54). Because of the small sample of rare infections, the type of infections decreased was not mentioned, but P. aeruginosa and non-tuberculous mycobacterial infections were diminished. In addition, the secondary endpoints of the study showed a decrease in healthcare visits in different places by 3.51 (95% CI −4.55 to −2.47), a change in the number of days with an outpatient antibiotic supply, −0.78 (95% CI −0.81 to −0.43) and a change in days of antibiotic use, −16.08 (95% CI −22.5 to −9.66) [17].
Migliorisi et al. recorded the microbiological data from the sputum samples of CF patients in the ELX/TEZ/IVA group and the control group. After one year of the triple combination treatment, the colonization rates of respiratory samples progressively decreased and almost 45.3% of the sputum samples of patients in the ELX/TEZ/IVA group became negative for pathogenic bacteria [13].
CF patients suffer from gastrointestinal symptoms such as abdominal pain, bloating or nausea, so Mainz et al. conducted a multi-center prospective study with 152 participants aiming to assess any differences in abdominal symptoms. They used the CFAbd-Score in patients treated with ELX/TEZ/IVA treatment and compared them to healthy controls. The CFAbd-Score consists of five domains: pain, gastro-esophageal reflux disease (GERD), quality of life impairment (QoL), disorders of bowel movement (DBM) and disorders of appetite (DA). After 24 weeks in the triple combination treatment, the total CFAbd-Score decreased significantly by 19%, the pain by 22%, the GERD by 20%, the DBM by 12%, the QoL impairment by 28% and the DA by 39% (all p < 0.05). However, in comparison to healthy controls, the total CFAbd-Score and the following domains, pain, GERD, DA, QoL, of PwCF during the ELX/TEZ/IVA treatment showed no significant differences. On the other hand, the DBM domain was significantly elevated during the triple therapy compared to the control group (17.6 ± 1.3 and 11.9 ± 1.4, p = 0.004, respectively). Meteorism and abdominal pain were the two most common symptoms that decreased from 60% to 50% and 59% to 39%, respectively, after triple treatment initiation [16].

Safety of Elexacaftor-Tezacaftor-Ivacaftor
The safety of the triple combination treatment was assessed by Keating et al. In their study, 92% of patients in the ELX/TEZ/IVA group, 100% of people in the placebo group and 71% of patients in TEZ/IVA group reported at least one adverse event (AE). Patients who received ELX/TEZ/IVA had mild events (53%), moderate events (43%) and serious events (4%). The most frequent side effects observed in patients who received the triple therapy were cough, increased sputum production, pulmonary exacerbations, hemoptysis and pyrexia. Elevated levels of aminotransferase greater than three times the upper limit occurred in 8%, and elevated bilirubin levels greater than two times the upper limit occurred in 3% of patients in this group. Concerning the serious side effects, cases of infective pulmonary exacerbation, distal intestinal obstruction syndrome and jugular venous thrombosis were noticed. No deaths occurred, but side effects such as rash, elevated bilirubin levels and chest pain, that occurred in three patients in ELX/TEZ/IVA group, led to the discontinuation of the trial. The administration of the triple combination was stopped in three patients because of adverse effects: elevated levels of SGOT, SGPT, CPK and myopathy in the first; elevated levels of bilirubin in the second; and constipation in the third [9]. Middleton et al. described the AE that occurred during their study, in which 93.1% of patients in the ELX/TEZ/IV group showed at least one, compared to 96% in the placebo group. The majority of patients in the ELX/TEZ/IVA group had mild (33.2%) and moderate (50.5%) AE and only 13.9% had a serious AE (ex. infective pulmonary exacerbation) compared to the control group (20.9% with a serious AE). In previous studies for other CFTR modulator therapy, rash and elevated levels of aminotransferase were observed, so these specific side effects were also assessed in this trial. A total of 10.9% of patients in ELX/TEZ/IVA group had elevated aminotransferase levels, mostly greater than three times the upper normal range (7.9%), compared to 4% in the placebo group. As for rash, it occurred in 10.9% of patients in the ELX/TEZ/IVA group and 6.5% in the control group. Moreover, elevated CPK levels were noticed, mostly associated with exercise, and changes in blood pressure (systolic and diastolic blood pressure increased by 3.1 mmHg and 1.9 mmHg, respectively), at week 24. No deaths were observed, but two patients in ELX/TEZ/IVA group discontinued the trial because of a rash in one patient and portal hypertension in another with cirrhosis [10].
Heijerman et al. noted that ELX/TEZ/IVA was generally well tolerated in a 4-week trial. Side effects were seen in 58% of participants in the ELX/TEZ/IVA group and 33% in the TEZ/IVA group. The side effects were mostly mild and moderate; serious AE occurred in 4% of the patients in ELX/TEZ/IVA group (rash and pulmonary exacerbation) and 2% in TEZ/IVA group (pulmonary exacerbation). The most common side effects reported were cough (15% in ELX/TEZ/IVA group and 8% in TEZ/IVA group) and pulmonary exacerbation (2% and 12%, respectively). Elevated levels of SGOT and SGPT greater than three, five or eight times the upper normal range occurred in 7%, 4% and 0% of the participants in the triple combination group, respectively, compared with no aminotransferase elevations in the TEZ/IVA group. A mild rash was observed in 4% of participants in the ELX/TEZ/IVA group and 4% in the control group. No deaths and no discontinuation of the trial in either treatment group were reported [11].
In the trial conducted by Barry et al.,66.7% of the patients in the ELX/TEZ/IVA group and 65.9% of those in the active control group (receiving Ivacaftor or Ivacaftor-Tezacaftor treatment) had at least one AE, mostly mild or moderate in severity. Serious AE were noticed in 3.8% of patients in the ELX/TEZ/IVA group and 8.7% in the control group. Elevated levels of aminotransferase occurred in 6.1% of patients in the ELX/TEZ/IVA group and 0.8% in the control group, and CPK levels increased in 1.5% and no patients, respectively. Rash, mild or moderate in severity, was seen in 3% of patients in the triple combination group and 4% in the control group. As for the blood pressure, the mean systolic and the mean diastolic pressure increased by 3 mmHg and 2.5 mmHg in the ELX/TEZ/IVA group and 0.5 mmHg and 0.3 mmHg in the control group, respectively, without any cases of hypertension in any group. The investigators did not notice any deaths, but the treatment was discontinued in one patient in the ELX/TEZ/IVA group because of elevated SGOT and SGPT levels and in two patients in the active control group due to anxiety, depression and pulmonary exacerbation [14].
In the phase 3b trial, conducted by Sutharsan et al., 89% of patients in the ELX/TEZ/IVA group and 92% in the TEZ/IVA group had an AE at week 24 of treatment, with the majority being mild or moderate in severity. The most common AE in the ELX/TEZ/IVA group was headache (29%) and nasopharyngitis (20%), and 6% of patients in the triple combination therapy and 16% in TEZ/IVA group had serious side effects. No deaths occurred, but one participant in the ELX/TEZ/IVA group discontinued the treatment owing to anxiety and depression, and two patients in the active control group due to psychotic disorder and obsessive-compulsive disorder. Elevated SGOT and SGPT levels greater than three times the upper normal level were reported in 6% of patients in the ELX/TEZ/IVA group and 6% in the TEZ/IVA group. Rash was observed in 13% of participants in the triple therapy group and 2% in the active control group. Increased levels of CPK were seen in 5% of patients in the ELX/TEZ/IVA group and 2% in the TEZ/IVA group. None of these side effects were serious and no treatment interruption was needed [12].
Mall et al. studied the safety of ELX/TEZ/IVA in children with CF aged 6-11 years. 80% of children in the ELX/TEZ/IVA group and 93.4% in the placebo group had AE, mostly mild and moderate in severity. The most frequent AE in the ELX/TEZ/IVA group were headache (30%) and cough (23.3%), whereas in the control group cough (42.6%), abdominal pain (27.9%), infective pulmonary exacerbation (26.2%), headache (19.7%), and oropharyngeal pain (19.7%); 6.7% of children in the triple combination group and 14.8% in the placebo group had serious side effects. Among children in the ELX/TEZ/IVA group, elevated levels of SGOT and SGPT more than three times the upper limit of normal, were noticed in 13.6% of patients, more than five times in 5.1%, and more than eight times in 1.7%. Among children in the placebo group, 4.9%, 1.6% and 0% had aminotransferase levels more than three, five or eight times the upper normal range, respectively. Concerning the rashes, 13.3% of children in the ELX/TEZ/IVA group and 4.9% in the placebo group had eruptions, but only one child in the triple combination therapy group discontinued the trial due to a serious rash. AE of hypertension and CPK levels increase occurred in no children in either group [15].
The above mentioned results are summarized in Table 1.

Efficacy of Elexacaftor-Tezacaftor-Ivacaftor
Pulmonary efficacy and effect on sweat chloride concentration DiMango et al., in a prospective cohort study with 43 patients with at least one copy of Phe508del mutation, noted that after 3 months of ELX/TEZ/IVA treatment the ppFEV 1 increased from 65% to 76% (p < 0.001) and the CFQ-R RD score was significantly improved [18].
Petersen et al. designed a study cohort in which they found that adults with CF treated with ELX/TEZ/IVA presented an annual rate of increase in ppFEV 1 of 7.81 points/year (95% CI 6.39-9.23, p < 0.0001) [23].
Growth and nutrition CFTR modulators have a beneficial effect on growth and weight gain, as shown by different studies. DiMango et al. observed that BMI was increased from 21.8 kg/m 2 (95% CI 21-22.6) to 22.7 kg/m 2 (95% CI 21.8-23.6, p < 0.001) in CF patients with at least one Phe508del allele after 3 months of triple combination treatment [18]. Furthermore, as noticed by Nichols et al. after 6 months of ELX/TEZ/IVA therapy in patients with at least one Phe508del allele, there was a BMI increase by 1.2 kg/m 2 from baseline for adults (95% CI 1.05-1.44) and 0.3 z-score in adolescents. Amelioration in BMI was similar in all subgroups, regardless of previous treatment [19]. Zemanick et al. noticed that BMI, BMI-for-age z-score, weight, weight-for-age z-score, and height, in children 6-11 years old with at least one Phe508del mutation, improved over the 24 weeks of ELX/TEZ/IVA treatment [22]. Petersen et al. conducted a single-center, retrospective, observational study with 134 adults with CF in order to assess the impact of ELX/TEZ/IVA treatment on body weight after 12.2 months of follow-up. The annual BMI change was 1.47 kg/m 2 /year (95% CI 1.08-1.87, p < 0.001) and the annual increase in body weight was 4.43 kg/year (95% CI 3.14-5.36, p < 0.001). It was noted that CF patients with pancreatic insufficiency had a more significant improvement in BMI after the triple therapy initiation compared to those with pancreatic sufficiency. Furthermore, the rate of BMI change of underweight patients and those with normal weight was decreased (from 7.5% to 2.2% and 65.7% to 56.7%, p < 0.001, respectively). On the contrary, the researchers observed an increase in the rate of BMI change of overweight patients from 19.4% to 31.3% (p < 0.001) and in obesity from 7.5% to 9.7%, p < 0.001) [23].
Other parameters i.

ii. Glycemic status
Researchers investigated the effect of the triple combination treatment on glucose tolerance and CFRD, given the fact that its impact on this domain is not well understood. Scully et al. performed a prospective, observational study with 34 adults with at least one Phe508del mutation and a history of exocrine pancreatic insufficiency, in which they used continuous glucose monitoring (CGM) sensors for 14 days before ELX/TEZ/IVA initiation and 3-12 months after therapy, with the purpose of assessing the effect of the triple CFTR modulator treatment on glycemic status (50% of the participants had already had CFRD). Overall, after the ELX/TEZ/IVA treatment, the CGM average glucose diminished to 124 ± 8 mg/dL from 136 ± 9 mg/dL (p < 0.018), percentage time >200 mg/dL decreased from 16.4 ± 4.1 to 9.7 ± 2.6 (p < 0.006) and the peak sensor value decreased to 280 ± 20 mg/dL from 306 ± 21 mg/dL (p < 0.045). No significant changes were noticed in measures of hypoglycemia, weight, or BMI. In subgroup measurements between candidates with and without CFRD, percentage time >200 mg/dL was significantly decreased in both groups. In patients with CFRD CGM, average glucose (AG) improved from 162 ± 10 to 144 ± 10 mg/dL (p < 0.033), % time 70-180 mg/dL from 63.6 ± 5.7 to 73.5 ± 5.3 mg/dL (p < 0.011) and weight increased from 67.7 ± 3.6 kg to 73.3 ± 3.6 kg (p < 0.045) after ELX/TEZ/IVA treatment [25].
Korten et al. carried out an observational pilot study with 16 CF patients ≥12 years with at least one Phe508del allele and without known CFRD, in whom they performed an oral glucose tolerance test (OGTT) before and 4 to 6 weeks after the start of ELX/TEZ/IVA treatment. Patients carried out a CGM system 3 days before till 7 days after initiation of the therapy. OGTT improved after the treatment (p < 0.02). Before treatment, five patients were categorized into normal glucose tolerance (NGT) group, two into intermediate glucose tolerance (INDET) group, six into impaired glucose tolerance (IGT) and two into CFRD group. After ELX/TEZ/IVA treatment, nine participants were classified in NGT category, four into INDET, two into IGT and there were no participants in the CFRD category. In addition, 60 min, 90 min, and 120 min plasma glucose significantly decreased after treatment (p < 0.03, p < 0.04, and p < 0.03, respectively); on the contrary, no changes were observed in fasting plasma glucose and in 180 min OGTT plasma glucose. Levels of 120 min insulin, 180 min insulin, and 180 min plasma C-peptide were improved under ELX/TEZ/IVA treatment (p < 0.01, p < 0.006, and p < 0.005, respectively). The area under the curve (AUC) was lower for blood glucose and blood insulin (p < 0.008, and p < 0.02) after ELX/TEZ/IVA initiation. No difference occurred in HbA 1 c with the triple combination therapy. As for the CGM results, the researchers noticed no difference in glucose levels before and after the triple treatment therapy [24].
Piona et al. performed a prospective, observational study with 21 CF patients aged ≥6 years, in order to assess the β-cell function (estimated by the derivative control (DC) = the response of β-cells to glucose increase, and by the proportional control (PC) = the response of β-cells to glucose concentration), insulin clearance and insulin sensitivity after CFTR modulator treatment. A total of five of the 21 patients, who had at least one Phe508del allele and severe lung disease (FEV 1 < 40%), had a spirometry, a SC test, and an OGTT 1-12 weeks before and 12-18 months after ELX/TEZ/IVA treatment. The results showed no significant change in β-cell DC, PC, insulin clearance, and insulin sensitivity after the triple therapy. Only HbA 1 c was significantly reduced in these patients (p = 0.04) [26].
Advanced Lung Disease (ALD) CF patients with advanced lung disease (ppFEV 1 < 40%) are usually excluded from clinical trials. However, given the very promising results of ELX/TEZ/IVA, researchers conducted studies that included patients with ALD. Stylemans et al. conducted a real-life follow-up study, in which they included 14 adult patients, Phe508del homozygous with ppFEV 1 < 30% or Phe508del/Minimal Function mutation genotype and with ppFEV 1 < 40%. Participants had a median age of 36 years, the majority of whom had a Phe508del/Phe508del genotype, all were diagnosed with pancreatic insufficiency and 50% had CFRD. After 4 weeks of treatment ppFEV 1 increased by 12 percentage points (p < 0.001) and remained stable thereafter. Median ppLCI decreased by 31% (p = 0.002) from baseline. Taking into consideration the significant amelioration of other markers, such as acinar ventilation heterogeneity, RV/TLC ratio, FVC, and V A , they concluded that there was a considerable ventilation distribution improvement. In addition, the exacerbation rate diminished from 0.33 to 0.07/month after 3 months of treatment [27].
Martin et al., using questionnaires, assessed the quality of life of patients ≥ 12 years old (median age: 35 years), having the following CFTR genotypes: Phe508del/Phe508del, Phe508del/other or unreported, and with ALD (ppFEV 1 < 40% and/or an indication for lung transplantation), after initiation of ELX/TEZ/IVA treatment. In general, after 4.3 (3.0-5.6) months of the triple combination treatment, patients reported an amelioration of pulmonary symptoms, a decrease in cough, sputum production, pulmonary exacerbations, IV antibiotics use, time spent on chest physiotherapy and suspension of lung transplantation discussions. They also reported an improvement in extrapulmonary symptoms, such as sleep quality and appetite, an amelioration in glycemic control, or increase in self-esteem [29].
Burgel et al., in a prospective observational study, assessed the impact of ELX/TEZ/IVA treatment in 245 patients aged ≥ 12 years (median age = 31 years) with at least one copy of the Phe508del mutation and ppFEV 1 < 40%, and/or being on the lung transplant waiting list or under transplantation evaluation. At 73 (32-88) days of ELX/TEZ/IVA treatment, ppFEV 1 increased by 15.1% (95% CI 13.8-16.4, p < 0.0001), with no significant difference in ppFEV 1 increase between those previously treated with a CFTR modulator and those not. Furthermore, ppFEV 1 had a greater increase in those without oxygen and/or noninvasive ventilation (NIV) at the beginning of the treatment. Specifically, ppFEV 1 increased by 16.2 points (95% CI 14.5-17.9, p < 0.0001) compared with those with oxygen and/or NIV before treatment (amelioration by +13.6%, 95% CI 11.6-15.7, p < 0.0001). As far as weight is concerned, this increased by 4.2 kg (95% CI 3.9-4.6, p < 0.0001), with a more significant increase in those not treated previously with a CFTR modulator (+4.5 kg, 95% CI 4.1-4.9, p < 0.0001) than those treated with another CFTR modulator (+3.4 kg, 95% CI 2.7-4, p < 0.0001). The ELX/TEZ/IVA therapy led to a decrease in other treatments; more specifically the number of patients who needed oxygen or enteral tube feeding was diminished by 50% (p < 0.001) and those in need of NIV by 30% (p < 0.001) [30].
The retrospective cohort study conducted by Carnovale et al. included 47 patients. All were aged ≥12 years (median age = 32 years old), had Phe508del/Minimal Function genotype, their ppFEV 1 was <40%, or they were on the waiting list for lung transplantation. Lung function was evaluated after 1 and 6 months of ELX/TEZ/IVA treatment. The ppFEV 1 increased by 10.69 percentage points (95% CI 8.05-13.33, p < 0.0001) and by 14.16 points (95% CI 11.43-16.89, p < 0.0001), after 1 and 6 months, respectively, from the baseline. The SCC decreased from a baseline of 91.1 mmol/lt to 52 mmol/lt (p < 0.00001) and to 46.2 mmol/lt (p < 0.001), after 1 and 6 months of treatment, respectively. CFQ-R RD score was ameliorated from a baseline of 55.5 to 83.3 (95% CI 50-100, p < 0.00001) after 1 month and to 91.6 (95% CI 61.1-100, p < 0.00001) after 6 months of therapy. A decrease of 77% in the annual rate of pulmonary exacerbations was reported due to the ELX/TEZ/IVA treatment and only one patient needed a single cycle of IV antibiotics. As for growth, the mean BMI at initiation was 20.7 kg/m 2 , which improved significantly to 21.4 kg/m 2 (p = 0.00005) and to 22.6 kg/m 2 (p < 0.00001) after 1 and 6 months of treatment, respectively [31].
As already known, ELX/TEZ/IVA treatment is safe and efficacious for patients ≥12 years old with at least one Phe508del mutation. Unfortunately, sometimes advanced lung disease is developed in early childhood, so there are children aged 6-11 years with a ppFEV 1 < 40%, requiring intense treatment or lung transplantation. Salvatore et al. evaluated the effectiveness and safety of the triple therapy after 24 weeks of treatment in this group of patients. In this retrospective, observational study, nine children aged 6-11 years, with a median age of 9.75 years, Phe508del homozygous or with a Phe508del/MF genotype, and with ppFEV 1 < 40%, participated. All had pancreatic insufficiency. The results showed a mean increase in ppFEV 1 37.79, p < 0.001) points from the baseline, after 24 weeks of treatment. The mean absolute change of BMI for age z-score was 0.60 (95% CI 0.33-0.87, p < 0.001), of weight for age z-score 0.41 (95% CI 0.20-0.62, p < 0.001) and of height for age z-score 0.31 (95% CI 0.05-0.57, p < 0.02), from baseline at week 24. The SCC significantly decreased by 74.8 (95% CI −62.44 to −87.07, p < 0.001) and the CFQ-R RD score increased to 100 (95% CI 100-100, p < 0.001) from the baseline value, over the 24 weeks of the study. Finally, an 80% lower rate of antibiotic use and zero hospitalizations were observed after 24 weeks of ELX/TEZ/IVA treatment [32].

Lung transplant perspectives
The CF patients included in the Bermingham et al. study with ALD had a history of lung transplant evaluation, but after the triple combination treatment seven patients were recategorized because they no longer met the criteria for lung transplantation due to their lung function improvement [28]. Similar results were found by Martin et al., as CF patients with ALD were taken off the lung transplantation candidate list after ELX/TEZ/IVA treatment [29]. Furthermore, 11 of 15 patients with severe lung disease who were on the transplantation list, after ELX/TEZ/IVA treatment were suspended, and 36 of 37, who were under evaluation for joining the list, no longer met the criteria for lung transplantation, according to the study conducted by Burgel et al. [30]. Another three patients in the study organized by Carnovale et al. decided to be removed from the lung transplantation waiting list after 6 months of ELX/TEZ/IVA treatment [31].

Safety of Elexacaftor-Tezacaftor-Ivacaftor
Zemanick et al. assessed the safety of ELX/TEZ/IVA treatment in children 6-11 years old, in whom 98.5% of the participants had at least one AE, 54.5% of which were mild and 42.4% moderate in severity. The most common AEs experienced by the candidates were cough (42.4%), headache (24.2%), and pyrexia (21.2%), 10.6% of the children presented elevated levels of aminotransferases greater than three times the upper normal range, and in 1.5% the levels were greater than five times the upper normal limit. As far as rashes are concerned, 24.2% of the patients had mild or moderate rash events (e.g., rash erythematous, rash maculopapular, rash papular, skin exfoliation, or urticaria). Due to the development of a rash after the first dose of the triple treatment, the drug was discontinued in one child. CPK levels were not greater than five times the upper normal limit. No AE of hypertension were noticed, the systolic blood pressure changed from −1.4 mmHg to 0.4 mmHg, and diastolic blood pressure from −0.3 mmHg to 1 mmHg, through the 24 weeks of treatment [22].
Researchers were concerned with the safety of triple combination therapy in CF patients with ALD. Stylemans et al., during the 3-month therapy, showed that it was well-tolerated and only one patient had a drug-induced liver injury leading to treatment discontinuation. No rash, dyspnea, or cough was observed [27]. A serious adverse event of pancreatitis and distal intestinal obstructive syndrome occurred in one patient who participated in the Bermingham et al. study, without interruption of the treatment; mild side effects, such as rashes, constipation, and hypoglycemia were seen in 10 participants [28]. Burgel et al. reported some side effects, generally mild, such as localized (7.2%) or generalized rashes (3.8%), headache (4.2%), gastrointestinal symptoms (10.2%), and myalgia (4.7%). Elevated levels of SGPT ≥ 3 times the upper limit of normal were noticed in 2.5% of patients and elevated levels of SGOT ≥ 3 times the upper limit of normal in 0.8%. Increased bilirubin (≥3 times the upper normal) was seen in 4.7% of participants (three of whom already had cirrhosis) and elevated CPK levels greater than three times the upper normal limit occurred in 3.4% of the patients. None needed to discontinue the triple combination therapy [30].
The above mentioned results are summarized in Table 2. -Adults with CF with at least one copy of Phe508del mutation (n = 43) -BMI improvement from 21.8 to 22.7 (p = 0.000002) -Increase in ppFEV 1 from 65% to 76% (p = 0.0000005) -Improvement of all domains of CFQ-R

Discussion
The CFTR modulator ELX/TEZ/IVA has been shown to be effective in Phe508del homozygous or Phe508del heterozygous with a minimal function mutation. The total number of included studies in this systematic review sums up the beneficial effects of this new medication.
Impaired lung function with a gradual deterioration, starting early in life, is a key feature of CF and ELX/TEZ/IVA improves pulmonary function significantly. Both clinical trials and observational studies highlight a substantial increase in FEV 1 , both in adults and children, after the initiation of treatment. LCI 2.5 , which is used to determine the ventilation inhomogeneity, also showed noteworthy improvements, when it was used as a surrogate of pulmonary function in studies. As for SCC, which is a clinical marker of CFTR function and is related to disease severity, the triple combination therapy showed that it can reduce its values even <30 mmol/lt.
The CFQ-R is a disease-specific health-related quality of life measure for children, adolescents, and adults with CF. It consists of 12 different domains, one of which concerns respiratory symptoms, which can be used in studies in order to assess the effect of the new therapies on the quality of life of CF patients. An increase in the CFQ-R RD score was observed with the new treatment. The use of ELX/TEZ/IVA also decreased the number of pulmonary exacerbations [34,35].
As far as metabolic parameters are concerned, ELX/TEZ/IVA promotes weight gain with an uncertain, but probably multi-factorial, mechanism. The new CFTR modulator ameliorates the appetite and augments food intake and weight gain. ELX/TEZ/IVA may rehabilitate part of the exocrine pancreatic function, leading to better intestinal absorption and weight gain. The increase in life expectancy in CF patients under the triple treatment results in a rising risk of hyperlipidemia and hypertension and is likely to increase the incidence of cardiovascular and cerebrovascular events [23].
The exact mechanism of CFRD and the role of CFTR modulators therapy in the pathophysiology of CFRD are not yet well defined. It is known that the dysfunction of insulin secretion causes CFRD. Even though CFTR protein is detected in pancreatic α and β-cells, implying a role in insulin secretion, this finding has not been confirmed by all studies. Indeed, minimal CFTR mRNA expression and CFTR protein were found in human islet cells. The impact of CFTR modulators on CFRD seems to be indirect; CFTR restoration could reduce the systemic and localized islet inflammation and, as a consequence, improve islet function and insulin sensitivity. In addition, a second possibility is the increased excretion of incretins from the gastrointestinal neuroendocrine cells, which enhance insulin secretion. On the other hand, improved calorie intake and intestinal absorption, due to CFTR modulator therapy, leads to weight gain and, as a result, increased insulin resistance. No clinical trials have evaluated the effect of ELX/TEZ/IVA on CFRD and glucose metabolism [36]. An observational study conducted by Scully et al. noticed an improvement in measures of hyperglycemia and glycemic variability with CGM after ELX/TEZ/IVA initiation [25]. Moreover, Korten et al. observed an improvement in endocrine pancreatic function with the triple modulator treatment as glucose tolerance for OGTT was improved [24].
Recent data on ADL in CF patients treated with ELX/TEZ/IVA have been very limited, because these patients are excluded from many studies, due to the adverse events and the unimportant lung function improvements noticed with previous CFTR modulators. However, positive events have been observed in small studies conducted in patients with ppFEV 1 < 40%. The results were encouraging, as ELX/TEZ/IVA treatment ameliorated the ppFEV 1 , the CFQ-R RD, and the BMI and diminished the SCC in adults and children. It is very important that, after initiation of the treatment, many patients with ALD no longer met the criteria for lung transplantation.
In general, as has been demonstrated by clinical trials and observational studies, ELX/TEZ/IVA is a well-tolerated medication in all the CF subgroups. Patients included in the aforementioned studies mostly suffered from mild to moderate adverse events.
The most frequent were cough, increased sputum production, pulmonary exacerbations, hemoptysis, and pyrexia. It was found that the increased fluidity of respiratory mucus after the ELX/TEZ/IVA initiation is responsible for cough and sputum production aggravation. Rashes (erythematous, maculopapular, papular, skin exfoliation, or urticaria) were a common side effect that occurred approximately in 4-10% of patients treated with ELX/TEZ/IVA. The exact mechanism of this event is unclear. Most likely, skin eruptions are mild to moderate in severity, but some important rashes may demand discontinuation of the triple CFTR modulator treatment. Elevations in blood pressure were noticed [10,23]. The role of CFTR modulator in vascular homeostasis is not known, as the direct effect of ELX/TEZ/IVA on non-epithelial cells is not yet understood. It has been hypothesized that CF patients have lower blood pressure because of the salt losses in their sweat, and consequently the improvement of CFTR function with the treatment leads to less salt wasting and higher levels of blood pressure [37][38][39].
Elevated levels of aminotransferases were noted in adults and children with CF and this was a common AE, which did not lead to treatment discontinuation. CPK levels were also found to increase, mostly in association with exercise. As far as gastrointestinal side effects of ELX/TEZ/IVA are concerned, one serious adverse event is distal intestinal obstruction syndrome (DIOS), which is mentioned in the clinical trial conducted by Middleton et al. [10]. It is already known that CF patients suffer from constipation, due to the thick intestinal mucus, intestinal mobility disorders, and indigested food being attached to the intestinal walls. After treatment initiation, the amelioration of the mucus hydration leads to fecal detachment of the bowel wall and its movement through the intestine, increasing the possibility of DIOS. In addition, the viscous bile with abnormal pH causes bile salts accumulation and bile gallstones formation, though the CFTR function restoration in the biliary epithelium, with the new treatment, leads to increased bile fluidity that could trigger the movement of pre-existing gallstones and subsequently the appearance of biliary colic and/or acute or chronic cholecystitis [37,[40][41][42][43]. Testicular pain is another side effect described by Rotolo et al., as the thinner mucus blockage moves from either testes, vas deferens, or both when electrolytes balance is achieved with CFTR restoration [44]. In addition, Miller et al. described two cases with both papilledema and hypervitaminosis A after ELX/TEZ/IVA treatment, which was related to the elevated absorption of vitamin A supplements; given the known correlation of vitamin A and increased intracranial pressure (ICP), they supposed that hypervitaminosis A led to increased ICP [45]. Moreover, mental health issues, such as anxiety, depression, psychotic disorder, or obsessive-compulsive disorder, were reported by Barry et al. and Sutharsan et al. [12,14]. The exact mechanism of action remains unclear; it is probably related to the fact that this medication has a lipophilic nature; it passes through the blood-brain barrier and interacts with the CFTR or the serotonin receptor 5-hydroxytryptamine 2c (5-HT 2c ), which has been associated with anxiety, depression, and suicidality. Even though IVA has a high to moderate affinity for the 5-HT 2c receptor, suggesting that this CFTR modulator has a positive action in the behavior, the adverse events observed pose the question as to whether ELX and TEZ have a serotonergic effect, which contradicts the positive effect of IVA [46,47].
Drug-induced liver injury (DILI) led to discontinuation of the ELX/TEZ/IVA treatment in one patient with CF and ALD, according to Stylemans et al. DILI is defined by one of the following thresholds: (i) ALT ≥ 5 times the upper normal limit, (ii) ALP ≥2 times the upper normal limit with an elevation of γ-GT or (iii) ALT ≥ 3 times the upper normal limit and elevation of TBIL ≥ 2 times the upper normal limit. DILI can be intrinsic (dosedependent, with an immediate effect, hours to days) or idiosyncratic (not dose-related and with a variable latency of onset of days to weeks). Interruption of the treatment is the intervention of choice in this case, but in critical patients with the need for non-replaceable drugs, favorable results have been noticed [48].
The development of the new CFTR modulators changed the natural course of the disease. Patients carrying at least one allele of the Phe508del mutation are eligible for the new therapies. Even though it is the most common CFTR mutation, with 85.5% of patients worldwide having at least one copy (44.1% are Phe508del homozygous and 41.4% are Phe508del heterozygous), there is a 14.5% of patients without any Phe508del mutation or with an unknown mutation [24]. This is the reason that individualized treatment is necessary. In this direction, international studies using intestinal organoids or nasal cells of CF patients and rare mutations, in order to assess their response to the novel molecules, are in progress. Research has demonstrated that results derived from ex vivo testing correlate fairly well with in vivo therapeutic changes and can be used as predictors of the clinical effectiveness of new drugs [49][50][51][52][53].

Conclusions
The new CFTR modulator has many positive effects on CF patients with at least one Phe508del allele, on their lung function, nutrition, quality of life, glycemic status, and other parameters. Even patients with ALD can benefit from the ELX/TEZ/IVA treatment and many have been suspended from the waiting list for lung transplantation. It is also proven that this new triple CFTR treatment is well tolerated with a favorable safety profile in all the subgroups of patients. Further studies are needed to establish the effect of this treatment on the rest of the CF manifestations (for example glycemic status, pancreatic insufficiency, fertility). As this new CFTR modulator is highly effective for patients with Phe508del mutations, a question has been raised as to whether it could be used in patients with rare CFTR mutations who have no indication for CFTR modulator treatment [54]. In this direction, studies with nasal cells and intestinal organoids from patients with rare mutations are in progress.